Date: Jan 19, 2009 7:50 PM
Author: matt271829-news@yahoo.co.uk
Subject: Re: Circular functions
On Jan 19, 11:44 pm, Albert <albert.xtheunkno...@gmail.com> wrote:

> On Jan 20, 10:25 am, Matt <matt271829-n...@yahoo.co.uk> wrote:

>

> > You've seen that cos(angle) = x/r

> <snip>

> > If the angle is 90 degrees then what is the

> > corresponding value of x?

>

> Now I see: x is zero and therefore cos90 = 0.

Correct.

Possibly I'm just repeating what's already been said, but imagine a

ray of length 1 that has one end fixed at the origin, and the other

end sweeping out a circle of radius 1. The x-coordinate of the free

end is cos(A), and the y-coordinate is sin(A), where A is the angle

the ray makes with the positive x-axis.

Anticlockwise rotation from the positive x-axis means a positive

angle; clockwise rotation means a negative angle. Once you've gone

around a full circle (2*pi radians, 360 degrees) you're back where you

started, so sine and cosine are periodic with period 2*pi.